Abstract: Conducting a research on the hydrochemical characteristics and genetic of coastal groundwater has significant implications for the rational development and utilization of coastal water resources and the prevention and control of pollution. In this paper, the groundwater chemical characteristics and genetic mechanism of Sandu Bay coastal zone in Ningde were studied by means of systematic groundwater sampling and analysis, statistical analysis, Piper graph, Gibbs diagram, ion ratio method, mineral saturation index method and hydrogeochemical phase map. The results show that the hydrochemical types of groundwater in the study area are mainly HCO₃-Ca type and mixed type, and the hydrochemical characteristics of groundwater are mainly affected by rock weathering process and cation exchange process, in which rock weathering process is mainly the dissolution of silicate minerals, while dissolution of carbonate and sulfate minerals also occurs simultaneously. To a certain extent, seawater mixing affects the hydrochemical characteristics of coastal phreatic water and confined groundwater, With about 27.5% of the groundwater samples showing a tendency of seawater mixing. The concentration of nitrate in phreatic water is high, which may be affected by human activities. The results of this research can provide critical evidence for the sustainable development and protection of groundwater resources in coastal areas.